Deftly playing on the worst fears of apartment-dwellers everywhere, this nasty little Spanish thriller explores just how bad things could really get as creepy building concierge César (Luis Tosar) stalks perky resident Clara (Marta Etura), aiming to drive her over the edge.

“The only thing that helps me is that others are unhappy, too,” narrates César, who lurks patiently under Clara’s bed to chloroform her nightly before infesting her cupboards with roaches, poisoning her body lotion and curling up next to her in bed. Clara, who only knows she feels oddly groggy in the mornings, insistently shrugs off what she sees as simply a run of bad luck. The game is on.

Horror director Jaume Balagueró takes a page or two from Hitchcock in this shudder-inducing narrative — especially in César’s devotion to his (suspiciously) comatose mom, and a pivotal bathtub scene. Ultimately, “Sleep Tight” makes a sounder case for nocturnal Webcams than the “Paranormal Activity” franchise ever could.